Electronic rf switch



Jan. 29, 1963 c. v. PARKER 3,076,155 ELECTRONIC RF SWITCH Filed May 31, 1962 INVENTOR CARLYLE V. PARKER United states ice . 3,076,155 ELECTRONIC RF SWITCH Carlyle V. Parker, Wellington Park, Va., assignor to the United States of America as represented by the Secretary of the Navy Filed May 31, 1962, Ser. No. 199,200 3 Claims. (Cl. 333-7) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to high speed radio frequency switches intended to control the delivery of substantial amounts of energy. In more particularity the invention relates to gas tube switching devices which are, of course, well known in such applications, however, a unique arrangement of tubes is employed to avoid switching delays caused by the substantial and unavoidable deionization time of gas tubes in such high speed switching applications.

Gas tubes have been employed for many years in the transmit-receive switching devices of radar systems. These devices have no mechanical inertia and hence are not limited by mechanical considerations, however, the low impedance conductive properties of such gas tubes depend upon the ionization effects of specially selected gases andthe ionization of gases is not instantaneous, nor is the deionization of such ionized gases instantaneous. In conventional radar applications the ionization and deionization times are not particularly troublesome, however in various developing fields, such as operation with radar pulses of a fraction of a millisecond the delay times are significant. A characteristic of gas tubes is that the ionization time is substantially shorter than the deionization time so that while a fast on operation is possible, the otf operation is significantly longer.. The invention is directed to an area of operations in which the shorter ionization delay is acceptable, but the longer deionization delay is not acceptable. The invention seeks to avoid the switching oil, or deionization, delay which is, as noted, significantly larger.

It is, accordingly, an object of the present invention to provide a gas tube switching circuit in which the delay inherent in the deionization time of the gas tubes is avoided.

Another object of the present invention is to provide an improved antenna switching circuit in which switching from one antenna to another is accomplished by the firing of gas discharge tubes which produce selective short circuiting of resonant transmission line sections.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein: 1 FIG. 1 of the drawing indicates a schematic presentation of apparatus constructed in accordance with the teachings of the present invention. It is observed that the showing of FIG. 1 is basically a schematic in which transmission lines involved therein are represented by single lines, whereas in accordance with established techniques, they could be conventional radio frequency transmission lines such aswaveguides, coaxial cable lines, twowire open lines, or the like.

FIG. 2 of the drawing shows a typical structure of a gas switch tube suitable for use in the apparatus of FIG. 1.

With reference now to FIG. 1 of the drawing the apparatus shown therein contains two load devices typically, antennas 10 and 11 which are connected to a power source such as transmitter 12 by means of a transmission line system. In this system it is desired that a switching capability be realized in which one antenna, typically antenna 10, may be substantially continuously operative except for brief instants of time during which operation of antenna 11 is desired to the exclusion of antenna 10. Usually the two antennas 10 and 11 would have dissimilar characteristics as regards pattern or the like, antenna 11, for example, being highly directive in one direction whereas antenna 10 could be omnidirectional, at least in one plane, or vice versa, depending upon the specific characteristics desired.

The apparatus of FIG. 1 contains three basic trans mission line junctions 13, 14 and 15, the junctions 13 and 14 being spaced a quarter wavelength apart and likewise junctions 14 and 15 being spaced a quarter wavelength apart. Junction 13 is connected to antenna 10 and junction 15 is connected to antenna 11. The sections of transmission line between junctions 13 and antenna 10 and between junction 15 and antenna 11 are not of critical length in terms of wavelengths or fractions thereof except as might be dictated by some time or phase relationship desired in the emission from the antennas 10 and 11. Actually, this phasing or time relationship is not necessarily a primary objective of the present invention which is directed more to the rapid switching of power from transmitter 12 between antennas 10 and 11. Further, as regards line lengths, the transmitter 12 is con-' nected to junction point 14 by a section oftransmission line 18 which is operative in a matched condition to avoid reflections from the point v14 to the transmitter 12.

A first stub line section consisting of portions 19, 20, and 21 is connected to junction13. Each of these line sections is a quarter wavelength long with an ionizable switch device 22 disposed between lines 19 and 20 and a second ionizable switch device 23 disposed between line section 20 and 21. A short circuit termination 24 is located at the end of line section 21. Leads 25 and 26 are shown connected to the ionizable devices 22 and 23 by means of which the ionization condition therein and hence the conductivity potential thereof may be controlled.

A second line stub, this one connected to junction 15 contains also three line portions 27, 28 and 29, line portion 27 being of a half wavelength and connected to junction 15, portions 28 and 29 each being of a quarter wavelength. Between line portions 27 and 28 is disposed an ionizable switch device 30, a second ionizable switch device 31 being disposed between the line portions 28 and 29, and a short circuit termination 32 being placed at the end of line portion 29. As with the other stub, control leads 33 and 34 are shown connected to the ionizable switch devices 30 and 31 by means of which the ionization conditions may be controlled to eifect conductivity changes therein.

The ionizable switch devices 22, 23, 30 and 31 are typically gas tube devices similar to those employed for TR switches in radar systems, and shown in greater detail in FIG. 2 which will be described at a subsequent point in the specification. For the present, sufiice it to say that these devices contain an ionizable gas which is in either of two states, namely, ionization or nonionization. In the ionization state, the ionizable switch device provides eifectively a short circuit across the transmission line at its point of location whereas in the nonionized condition the gas tube is virtually a continuous matched transmission line circuit and hence has no significant effect upon the impedance matching or mismatching. conditions of the transmission lines at the points of 10-, cation of the various ionizable devices.

Control of the ionization condition of the ionizable switch devices is normally by means of a third element which has applied to it a voltage usually of a D.-C. or pulsed D.-C. nature to initiate ionization within the tube,

When the tube is ionized by the application of such a control signal, the ionization condition prevails so that conductivity thereof to a radio frequency field applied thereto will exist. in the reverse condition of the control signal for the gas tubes, the tubes are nonionized hence nonconductive to a radio frequency voltage applied. By thus applying or removing the control signal voltage, it is possible to cause the ionizable'switch devices to be either conductive or nonconductive to radio frequency energy and hence switching action thereof is obtained.

The mechanism by which switching action in the ionizable switch tubes produces switching and specifically avoids switching delays due to the relatively long deionization time of the ionizable devices is described in the following paragraphs.

A first condition may be selected wherein none of the ionizable switch devices 22, 23, 30 and 31 is conductive. Under these conditions, the three-quarter wavelength stub of line portions 19, 20 and 21, short circuit terminated as it is at point 24, presents a high impedance at junction 13 so that for all practical purposes it is of no significance at point 13. Under these conditions, the transmission line from junction 14 to antenna is virtually flat throughout so that antenna 10 is connected to junction point 14 in a matched impedance condition, which condition continues through line 18 to transmitter 12. At the same time, however, the stub consisting of line sections 27, 28 and 29, being of a full wavelength dimension and short circuited at 32 reflects a low impedance at junction so that the line leading from junction 14 to antenna 12 is effectively shorted at junction 15. This short is transformed through the quarter wavelength section between junctions 15 and 14 appearing at junction 14 as a high impedance and hence it is ineffective to unbalance the balanced condition at junction 14 extending from transmitter 12 to antenna 10. With the line leading from junction 14 to antenna 11 thus appearing as a high impedance there is virtually a complete absence of energy delivery to antenna 11 from transmitter 12.

A second condition of operation in the antenna device of FIG. 1 may be analyzed wherein ionizable switch devices 23 and 31 are both rendered ionized by the application of an appropriate signal to lines 26 and 34. in this second condition the line stub connected to junction 13 is effectively short circuited not only at the termination 24, but also at the ionizable device 23. With the short circuit thus occurring at the ionizable device 23, the stub connected to junction 13 is effectively only a half-wavelength long and the short at 23 is reflected to junction 13 as a short across the transmission line leading from junction 14 to antenna 10. This short circuit at junction 13 is reflected and transformed by the quarterwave line section from junction 13 to junction 14 so that the entire line leading from junction 14 to the antenna 10 appears as a high impedance and hence, incapable of receiving any substantial amount of radio frequency energy.

At the same time as the foregoing in this second condition, the ionizable switch device 31 presents a short circuit at that point which is reflected at junction 15, three-quarters of a wavelength away, as a high impedance circuit. Thus, the open circuit impedance reflected by the stub connected to junction 15 receives substantially no energy so that the line section from junction 14 to antenna 11 can operate as a virtually fiat line with efficient power delivery from transmitter 12 to antenna 11.

The foregoing second condition is brought about very quickly by applying a unit function of voltage to the lines 26 and 34, ionization of the devices 23 and 31 taking place in an acceptably short period of time.

The third condition of the apparatus of FIG. 1 to be described is that which will occur immediately upon the ionization of the ionizable devices 22 and 30 by the ap plication of suitable unit function ionizing potentials to the lines 25 and 33. With devices 22 and30 thus ionized,

the stub connected to junction 13 is merely the quarterwave long portion 19 which presents a high impedance to junction 13 and hence does not upset the fiat line impedance matched condition between junction 14 and antenna 10. At the same time with switch device 30 ionized, this device being disposed a half-wave away from the junction 15, the stub line presents a short circuit impedance condition at junction 15, which zero impedance condition is transformed by the quarter wave line section between junction 15 and junction 14 so that the entire line section appears at junction 14 as a high impedance. Thus it does not receive any significant amount of energy. Under these conditions, then, antenna 10 is operative and antenna 11 is virtually inoperative.

The important thing to note at this point with regard to the invention is that this reversal of condition back to the original condition with antenna 10 operative is obtained with a delay solely dependent upon the ionization time of the devices 22 and 30 and is completely independent of the deionization time required for the previously ionized devices 23 and 31 which could continue to be conductive or ionized, for that matter, without any substantial efiect upon the delivery of power be tween the two antennas 10 and 11. Thus, in going through the conditions one, two and three, thus described, it is'seen that the overall device is caused to switch from an initial condition with antenna 10 operative to an interim condition with antenna 11 operative, and back to the initial condition with antenna 10 operative, both switching delays being determined by the ionization time of the ionizable switch devices 22, 23, 30 and 31, and independent of the comparatively long and unacceptable deionization time required for the devices 23 and 31.

A second one, two, three cycle of operations as described in the foregoing will encounter delays due to deionization time. The way this is involved is that another cycle to the two condition cannot occur until the ionizable switch devices 22 and 30 deionize. Normally this is not of a serious disadvantage because it is not normally the situation that the recurrence of the on period of antenna 11 is so rapid as to result in a separation between active periods of antenna 11 which is less than the deionization period for the ionization devices 22 and 30. However, it is possible to provide for such rapid switching as in double-pulsing operations of the antenna 11 or the like by providing additional pairs of ionizing devices 23, 3-1 and 22, 30, together with additional lengths of quarter-wave transmission lines in place of the shorts 24 and 32 which shorts would be located at the end of the stubs in any event. Thus, with four pairs of ionizing devices, it would be possible to double-pulse the antenna 11 for very short periods of time without any limitation as to deionization of the ionizable devices during the double-pulsing period. This principle can be extended as required.

Actually the repetition of the on-off cycle, regardless of it total number of occurrences, finds certain advantages where the ionizable devices begin to ionize upon the application of the control voltages to lines 25, 26, 33 and 34, and begin to deionize upon the withdrawal of such voltages, regardless of Whether or not the ionizable devices are actually receiving radio frequency currents from transmitter 12 at the same time. With this in mind, the cycle will then proceed to conduction by antenna 11 upon firing of the ionizable devices 23 and 31, return to energizing of antenna 10 when the ionizable devices 22 and 30 are ignited, at which time the control voltage to lines 26 and 34 by ionizable devices 23 and 31 can be removed to permit devices 23 and 31 to begin to deionize. At this point in time, it is then possible to remove the control voltages from lines 25 and 33 to resultin the ultimate deionization of devices 22 and 30 without affecting any significant change in the power division between the antennas 10 and 11.

spasms The way the foregoing comes about is as folldws: Noting that the devices 22 and 30 are actually a half wavelength from the corresponding short circuit termina tions 24 and 32 of the stubs, it is observed that with ionizable devices 23 and 31 inactive, the deionization of devices 22 and 30 will not produce any significant change in the pedance of the stubs as seen at the point 13 and '15, so that the deionization of devices 22 and 33 will not be accompanied by any change in antenna power. Thus, even with the mere two pair ap paratus of FIG. I, it is possible to experience various manipulations of the ionization and deionization periods to secure significant advantage in reduction of the deleterious efifect thereof.

With reference now to FIG. 2 of the drawings, a typical arrangement of individual ionization switch devices 22, 23, 31 and 30, is shown. A tube is essentially a triode with the space inside the tube between grid and anode, which is exposed to the R-F field, reduced to a minimum; and filled with a rare gas at a low pressure. The tube has an envelope 5b which is of some suitable glass material, together with 'a cathode 51, an anode 52, and a grid 53. The cathode can be heated if desired by suitable power supply connections 54 and 55. Connection to the grid 53 is by means of :a suitable disc 56 which is of some suitable material such as Kovar, having desirable properties of adhesion to the glass structure. The anode connection is through a suitable glass bead which covers an aperture in the disc 56 to permit the extension of the anode 52 into proximity to the cathode. Typically the distance between the inner end of the anode pin and the grid mesh is approximately one-thirty-second of an inch. The grid mesh is made of nickel screen having 40 wires to the inch in each direction. The tube interior typically contains argon gas at 150 microns pressure. The spacing of the grid mesh must be close enough to prevent a discharge in the grid-anode space when the control voltage is zero; the spacing must be wide enough, on the other hand, to provide a low R-F impedance between the grid and plate when the tube fires.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A transmission line stub capable of rapid impedance variation a plurality of times substantially independent of deionization delay of ionizable switch tube components comprising, a section of transmission line having first and second ends, said second end being short circuit terminated, at first ionizable switch tube connected across said transmission line between the first and second ends at a quarter wavelength from the termination, a second ionizable switch tube connected across said transmission line between the first end and the first ionizable '6 switch tube at a quarter wavelength from the first switch tube, and means for controlling the ionization of the switch tubes whereby the effective termination of the stub is at the second end when the switched tubes are nonionized, at the first switch tube when it is ionized and at the second switch tube when the second switched tube is ionized irrespective of the condition of the first switch tube.

2. In combination a power source, first and second load devices, a transmission line junction point connected to said power source, first and second transmission lines for connecting the junction point to the first and second load devices, respectively, a first stub line connected to said first transmission line at a point an odd multiple including unity of a quarter wavelength from the junction point, said first stub line containing in series a plurality of transmission line portions each an odd multiple including unity of .a quarter wavelength long, said first stub being impedance mismatch terminated and shunted at each junction of line portions by an ionizable switch device, a second stub line connected to said second transmission line at a point an odd multiple including unity of a quarter wavelength from the junction point, said second stub line containing in series a plurality of transmission line portions one being an even multiple including two of a quarter wavelength long, the others being an odd multiple including unity of a quarter wavelength long, said second stub being impedance mismatch terminated and shunted at each junction "of line portions by an ionizable switch device, and means for controlling the sequential ionization of said ionizable switch devices in pairs one in each stub beginning with the pair closest to the termination.

3. In combination a power source, first and second load devices, a transmission line junction point connected to said power source, first and second transmission lines for connecting the junction point to the first and second load devices, respectively, a first stub line of waveiength connected to said first transmission line at a point a quarter wavelength from the junction point, said first stub being short circuit terminated and shunted at each intermediate quarter wave point by an ionizable switch device, a second stub line of one wavelength connected to said second transmission line at a point a quarter wavelength from the junction point, said second stub being short circuit terminated and shunted at the quarter wave point from the termination and the half wave point from the termination by ionizable switch devices, and means for controlling the sequential ionization of said ionizable switch devices in pairs one in each stub beginning with the pair closest to the termination.

References (fitted in the file of this patent UNITED STATES PATENTS 2,656,534 Jackson Oct. 20, 1953 

2. IN COMBINATION A POWER SOURCE, FIRST AND SECOND LOAD DEVICES, A TRANSMISSION LINE JUNCTION POINT CONNECTED TO SAID POWER SOURCE, FIRST AND SECOND TRANSMISSION LINES FOR CONNECTING THE JUNCTION POINT TO THE FIRST AND SECOND LOAD DEVICES, RESPECTIVELY, A FIRST STUB LINE CONNECTED TO SAID FIRST TRANSMISSION LINE AT A POINT AN ODD MULTIPLE INCLUDING UNITY OF A QUARTER WAVELENGTH FROM THE JUNCTION POINT, SAID FIRST STUB LINE CONTAINING IN SERIES A PLURALITY OF TRANSMISSION LINE PORTIONS EACH AN ODD MULTIPLE INCLUDING UNITY OF A QUARTER WAVELENGTH LONG, SAID FIRST STUB BEING IMPEDANCE MISMATCH TERMINATED AND SHUNTED AT EACH JUNCTION OF LINE PORTIONS BY AN IONIZABLE SWITCH DEVICE, A SECOND STUB LINE CONNECTED TO SAID SECOND TRANSMISSION LINE AT A POINT AN ODD MULTIPLE INCLUDING UNITY OF A QUARTER WAVELENGTH FROM THE JUNCTION POINT, SAID SECOND STUB LINE CONTAINING IN SERIES A PLURALITY OF TRANSMISSION LINE PORTIONS ONE BEING AN EVEN MULTIPLE INCLUDING TWO OF A QUARTER WAVELENGTH LONG, THE OTHERS BEING AN ODD MULTIPLE INCLUDING UNITY OF A QUARTER WAVELENGTH LONG, SAID SECOND STUB BEING IMPEDANCE MISMATCH TERMINATED AND SHUNTED AT EACH JUNCTION OF LINE PORTIONS BY AN IONIZABLE SWITCH DEVICE, AND MEANS FOR CONTROLLING THE SEQUENTIAL IONIZATION OF SAID IONIZABLE SWITCH DEVICES IN PAIRS ONE IN EACH STUB BEGINNING WITH THE PAIR CLOSEST TO THE TERMINATION. 